1. Field of the Invention
The present invention relates to an audio player of a mobile communication terminal. More particularly, the present invention relates to a method and an apparatus for automatic volume control in an audio player of a mobile communication terminal, which adaptively controls the volume of the audio player according to environmental noise.
2. Description of the Related Art
Recently, technologies for reproducing audio files in order to listen to music by using mobile terminals are being widely used. However, when a user tries to reproduce audio files by using a mobile communication terminal in order to listen to music through an earphone or a headphone in a noisy environment such as subway train, street, park, etc., the user may experience great difficulty in listening to the music due to the surrounding noise. Especially, human auditory characteristics include a masking effect, which implies a phenomenon in that, from among audio signals sensed by auditory organs, a signal having a sufficiently large amplitude on the frequency axis or time axis covers small signals around the signal and prevents the small signals from being heard. In other words, in an environment in which background noise is larger than audio signals on the frequency axis or time axis, it is very hard or nearly impossible to hear the audio signal.
When a user listens to an audio signal by using a portable audio player in a noisy environment, such as street, etc., the user usually sets the volume as high as possible due to the background noise. Such a high volume may cause damage to the user's auditory organs and the background noise still disturbs hearing of the relatively small amplitude parts.
Recently, various technologies for eliminating such environmental noise have been proposed. One conventional technology for eliminating environmental noise is to use an earphone which includes a peripheral portion made from a special material in order to shield the user's auditory organ from the environment. This earphone basically intercepts the environmental noise in order to make the user hear only the intended audio signals. However, because the internal shapes or structures of ears are different according to each user, it is difficult to completely intercept the environmental noise and may cause inconvenience to users who have worn the earphone for a long time. Further, the conventional earphone is made from an expensive material and may cause the user to feel deafened just after wearing the earphone.
Another conventional technology for eliminating environmental noise is to use headphones, which receive environmental noise in real time by using a microphone attached to an exterior of the headphones and generate a signal with the same level and an inverse phase of those of the received real time noise inside of the headphone, thereby offsetting the environmental noise. This technology is called “Active Noise Cancellation.” In order to achieve the ANC inside of the headphones, it is necessary to invert the phase of the background noise input through the microphone and then generate a signal with the inverted phase inside of the headphones. These steps require a separate power source mounted in the headphones, which increases the power consumption. Further, addition of the power source increases the weight of the headphones and degrades their portability. Moreover, since the noise level in an inner environment and an outer environment of the headphones occasionally changes according to the wearing state of the headphones by the user, the noise may still remain inside of the headphones. Therefore, the conventional headphones are advantageous only for elimination of special noise rather than various kinds of unknown noise and are not useful for temporally changing noise.
Accordingly, there is a need for an improved method and apparatus for automatic volume control in a mobile communication terminal.